It would depend.
Thinking about it, a book would be a better medium for communicating some of the more complex/baffling/ambitious narratives that the series itself has struggled with. Such as XII, XIII and XV. Or Vagrant Story. Or Tactics. You know, those ones that are either extra wordy or required a datalog/post-release stuff/whole metaseries to understand a single story.
On the whole, provided it was treated seriously as a book, I'd pick up an original FF book, or competent novelisation of an existing game/universe.